Decline in Covid-19 cases adds to questions about waves of infections in South Africa

Since mid-January, confirmed Covid-19 infections in South Africa have dropped from a record nearly 22,000 a day to about 1,000, without a large-scale vaccination campaign or strict blockade. Less than 5% of Covid-19 tests show traces of the virus, a sign that health agencies lack fewer cases. The government has lifted most of the remaining virus restrictions for the country of 60 million people.

The cause of this sharp decline in cases remains somewhat a mystery. As in other countries that have seen surprising declines in Covid-19 cases – such as India, Pakistan and parts of Brazil – epidemiologists and virologists put together different explanations for why the outbreak in South Africa does not follow. models established elsewhere.

These range from important population groups that reach sufficient levels of immunity to slow down transmission, to those who more closely follow the rules of social distancing, such as wearing masks and voluntarily reducing contact, when deaths were on the rise before decline.

“Everyone confesses certainty [about why infections started dropping] mind, ”said Harry Moultrie, a senior epidemiologist at the National Institute of Communicable Diseases in South Africa or the NICD. “There is so much uncertainty in all of this.”

More than a year after the pandemic, there are still many scientists who do not know how the coronavirus moves through society, often creating waves of infections whose peaks coincide with overwhelmed hospitals and a large number of deaths. Meanwhile, in the gutters, life in some places can feel almost normal again.

Filling the gaps in the world’s understanding of the virus could have important implications for public health decisions. These include how to calibrate government interventions, such as blocking, where vaccines are best targeted and when a country or region has achieved herd immunity – or if this is even possible, given the emergence of vaccines. new coronavirus strains.

A complicated factor in South Africa, as in other countries, is that researchers do not know the true effect of the virus on the population. Due to limited testing capabilities and asymptomatic infections, there are no definitive data on how many people have recovered from Covid-19 and can now be immune.

Virologists continue to study the coronavirus variant, known as B. 1,351, which fueled the latest wave of infections here. The strain appears to make some existing vaccines less effective and, in some cases, has re-infected people who have recovered from a previous Covid-19 attack.

Unlike the crisis in many parts of Europe last summer, the current decline in infections in South Africa has not followed a strict government-imposed deadlock. At the end of the year, which overlaps with the main summer holidays of the southern hemisphere, the government closed the popular beaches, tightened the nightgown and banned large social gatherings and the sale of alcohol. A national mask mandate has been in force since April 2020.

However, indoor dining at limited capacity has been allowed around the world and many families have come together for Christmas and New Year. Most of the restrictions came only after tens of thousands of South Africans working in economic centers such as Johannesburg had already traveled to see family in provinces where the number of Covid-19 cases was double the July record. during the first wave. The return of workers home in early January, often crammed into common minibus taxis that are a common means of public transportation in South Africa, have created perfect conditions for the virus to spread.

The simplest explanation for the sharp drop in cases since mid-January is that sections of the population have reached a level of immunity that has made it harder for the virus to jump between different groups, said Jinal Bhiman, chief medical scientist at NICD. .

Only about 1.5 million South Africans, about 2.5% of the population, tested positive for Covid-19. But it is clear that the real level of infection was much higher. Since cases first began to rise in May, the country has seen more than 145,000 excess deaths, 85% to 95% of which are likely to be caused by Covid-19, according to the South African Medical Research Center. That means about one in 500 people in South Africa – where the average age is a decade below the US – have died of the disease in the past 10 months.

South African researchers, after testing the blood of 4,858 antibody donors in January, estimated that more than half of the 15- to 69-year-olds in the two most affected provinces had already had Covid-19. But immunity levels are unlikely to be as high in other parts of the country.

Experts also warned that blood donors are not representative of the global population, as evidenced by the recent recurrence of infections in the Brazilian city of Manaus, where an antibody study with blood donated last year found similar results.

In the absence of national herd immunity, scientists focus on the role of certain networks or individuals with numerous social or work contacts in leadership and, ultimately, slowing down localized outbreaks. “Highly sociable people get infected first, and the virus travels through these networks,” said Dr. Moultrie. When enough people in these networks become immune, the transmission goes off.

Researchers around the world are also studying the impact of voluntary changes in behavior, which can anticipate and strengthen government-imposed restrictions. “When rates rise, people change their behavior,” said Saad Omer, director of the Yale Institute for Global Health. Just as a small increase in social contacts can lead to an exponential increase in infections, reducing gatherings when infections are already declining can further accelerate the decline.

“Small changes can have massive consequences,” said Dr. Omer.

Perhaps the most difficult question to answer is what will happen next. Will cases increase again, probably fueled by another strain of coronavirus, as happened about two months after South Africa ended its first wave of infections in September? Juliet Pulliam, who heads the South African Center of Excellence in Epidemiological Modeling and Analysis, says there is no way to know.

“I don’t think it’s possible to predict with certainty when, or even if, there will be a third wave in South Africa,” she said.

Write to Gabriele Steinhauser to [email protected]